In this kind of semiconductor radiation detector, hitherto, high resistance bulk crystals such as cadmium telluride (CdTe) or cadmium zinc telluride (CdZnTe), excellent as radiation detecting materials have been used. In the case of high resistance bulk crystals of CdTe, it is hard to obtain crystals over a large area having homogeneous and excellent electrical characteristics, and usually a single element of a small volume of about 1×1×1 mm3 has been used or scores of them are arranged, and a radiation detector of a small array type is used. When such bulk crystals are used, it is technically difficult to realize a radiation detector for an area large enough to cover the entire chest area of a human body, and it is also very expensive. Further, in the case of radiation detectors based on conventional high resistance bulk crystals of CdTe, conductive electrodes or Schottky electrodes are formed on the upper sides and undersides of the crystals, a high voltage of hundreds to 1000 V is applied between the two electrodes, and the carrier generated by radiation in the CdTe crystals is extracted by an electric field and detected as an electrical signal. Therefore, in this kind of radiation detector using high resistance bulk crystals of CdTe, it is scarcely possible to improve detection characteristics except in terms of the resistance of the element.
In contrast, Japanese Patent Application Laid-Open No. 64-89471 discloses a semiconductor radiation detector having a hetero junction made up of a compound semiconductor crystals of CdTe or the like, and a crystalline thin film of InAs or the like. In the case of this semiconductor radiation detector, the compound semiconductor crystal is used as an active region (active layer) for generating the carrier, and the crystalline thin film layer has a function of implanting the carrier efficiently from the compound semiconductor crystal into the metal electrode. Therefore, if crystal of a II-VI group such as CdTe are used for the compound semiconductor crystal, it is very hard to obtain a crystal covering a large area, and the semiconductor radiation detector becomes very expensive. If on the other hand crystals other than CdTe or CdZnTe are used for the compound semiconductor crystal, radiation-detecting characteristics are not sufficient.
Japanese Patent Application Laid-Open No. 6-120549 discloses a radiation detector composed of semi-insulating semiconductor crystals such as CdTe, a P-type P—HgCdTe epitaxially grown at one of its sides, and an N-type N—HgCdTe epitaxially grown at the other side. In this semiconductor radiation detector, the same problems as in the case of the semiconductor radiation detector disclosed in Japanese Patent Application Laid-Open No. 6-120549 are present because the semi-insulating semiconductor crystals such as CdTe are used as an active region for generating the carrier.
The invention is devised to solve the problems of the prior art, and it is hence an object thereof to present a semiconductor radiation detector excellent in radiation detection performance, having a sufficient strength, capable of being formed over a large area, and manufactured inexpensively; and a method of manufacturing the same.